As broadcasters continue the transition from analog to digital video, the television production process is increasingly conducted in an all-digital domain, that is, from the initial camera shot to the display in the consumer's living room. This move to digital technology permits broadcasters to simultaneously broadcast multiple video streams using a single connection. Indeed, for popular live events, broadcasters typically deploy mobile broadcast units to route and manipulate, i.e. producing, the numerous video streams, which come from respective cameras throughout the event, before being transmitted.
An approach to manipulating and monitoring the video streams is a multiviewer. The typical multiviewer may include a monitor and associated processor receiving the video streams. Each video stream typically comprises a high-resolution digital video stream. Accordingly, the processor may perform the computationally intensive operation of scaling the video stream to accommodate simultaneously fitting all the video streams onto a single display. Some multiviewers may use a plurality of monitors, thereby permitting the viewing of even more video streams. A potential drawback to the typical multiviewer is the difficulty in rearranging the video streams on the monitor in real time. For example, a user viewing the multiviewer monitor displaying four video streams split equally over quarters of the monitor may desire to expand a first video stream and correspondingly reduce the other video streams. This operation may cause the processor to adjust scaling operations in real time based upon requests from the user. More specifically, to provide advanced features to the user, the typical multiviewer may have to include significant hardware to provide adequate processing power, thereby possibly increasing the form factor and housing size to undesirable levels.
An approach to scaling used by multiviewers available from Evertz Microsystems Ltd. of Burlington Canada is full input scaling. Using full input scaling, the video streams are completely scaled before being compressed and combined into a transport stream for viewing by the monitor. Potential drawbacks to the full input scaling approach may include significant hardware requirements that exceed mobile packaging environments. Moreover, each desired scaled size for the video streams may use dedicated hardware. Moreover, the transport stream may have limited bandwidth and may be incapable of displaying the video streams in their native resolution without upconverting the video streams, which may impact the quality thereof.
Another approach to scaling used by certain multiviewers available from the Harris Corp. of Melbourne, Fla., the assignee of the present application, is cascading. This approach may include coupling full scaler modules in cascade, each module being responsible for scaling a video stream and superimposing the respective stream onto the transport stream, i.e. the user display. Several drawbacks to this approach may include burdensome system level control, difficult output scalability, large hardware requirements, and a failure intolerant design.
Yet another approach to scaling in multiviewers is destination scaling in hardware. In this approach, the scalers are located downstream from the routing devices, for example, cross-point switchers. Several drawbacks to this approach may include lack of modularity, inefficient hardware consumption, and large form factor for the housing, and limited input and output scaling.
Another approach to scaling in multiviewers is destination scaling in the Graphics Processing Unit (GPU). In this approach, the video streams are directly fed via a Direct Memory Access (DMA) module into the central processing unit (CPU) of a personal computer, where any needed pre-processing is performed. The video streams are then rendered onto the monitor using the GPU. Several drawbacks to this approach include support for only few video streams, limited bandwidth in the DMA module, and lack of scalability in the input and output.
Another approach to a multiviewer is disclosed in U.S. Pat. No. 7,023,488 to Szybiak et al. This multiviewer includes a circuit for detecting a transition in the content of a digital video stream containing embedded audio samples and for providing a smooth transition from an old audio stream embedded before the transition to a new audio stream embedded after the transition.